Personalized tourniquet for intermittent vascular occlusion

ABSTRACT

An apparatus for intermittent vascular occlusion based on a personalized tourniquet pressure (PTP) includes a dual-purpose tourniquet cuff having an inflatable bladder, a sensor module having a pulsation sensor communicating pneumatically with the inflatable bladder for sensing and characterizing pressure pulsations indicative of a distal occlusion pressure (DOP) to identify a minimum pressure at which penetration of blood past the cuff is stopped, a PTP estimator responsive to the pulsation sensor for producing an estimate of a PTP, wherein the estimate of the PTP is a function of the DOP, an effector module communicating pneumatically with the inflatable bladder for maintaining pressure in the bladder near the PTP during a first time period and for maintaining pressure in the bladder near a second level of pressure during a second time period, and a controller selectively operating the inflatable bladder in conjunction with the sensor module and the effector module.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/837,999, filed Apr. 27, 2015, which is acontinuation-in-part of U.S. patent application Ser. No. 14/696,401,filed Apr. 25, 2015, now U.S. Pat. No. 9,814,467, which is acontinuation of U.S. patent application Ser. No. 14/328,607, filed Jul.10, 2014, now U.S. Pat. No. 9,039,730, all of which are incorporatedherein by reference.

FIELD

This invention pertains to pneumatic tourniquet systems commonly usedfor stopping the penetration of arterial blood into a region of apatient to facilitate the performance of a surgical or medicalprocedure. In particular, this invention pertains to a pneumatictourniquet methods and apparatus for establishing and maintaining apersonalized tourniquet pressure for a period of time.

BACKGROUND

Surgical tourniquet systems are commonly used to stop the penetration ofarterial blood into a portion or region of a patient's limb, thuscreating a clear, dry surgical field that facilitates the performance ofa surgical procedure and improves outcomes. A typical surgicaltourniquet system of the prior art includes a tourniquet cuff forencircling a patient's limb at a desired location, a tourniquetinstrument, and flexible tubing connecting the cuff to the instrument.In some surgical tourniquet systems of the prior art, the tourniquetcuff includes an inflatable bladder that is connected pneumatically to atourniquet instrument via flexible tubing attached to one or two cuffports. The tourniquet instrument includes a pressure regulator tomaintain the pressure in the inflatable bladder of the cuff near areference pressure that is above a minimum pressure required to stoparterial blood penetration past the cuff, when applied to a patient'slimb at a desired location during a time period suitably long for theperformance of a surgical procedure. Many types of such pneumaticsurgical tourniquet systems have been described in the prior art, suchas those described by McEwen in U.S. Pat. Nos. 4,469,099, 4,479,494,5,439,477 and by McEwen and Jameson in U.S. Pat. Nos. 5,556,415 and5,855,589.

Tourniquet cuffs of the prior art are designed to serve as effectorswhich apply high pressures that stop the penetration of arterial bloodpast the applied cuff for surgical time periods which can extend from afew minutes to several hours. Tourniquet cuffs of the prior art differsubstantially from pneumatic cuffs designed and used for other purposes.For example, pneumatic cuffs employed in the intermittent measurement ofblood pressure are typically designed to apply much lower pressures formuch shorter periods of time to selected arteries beneath an inflatablebladder portion of the cuff that does not surround the limb; such cuffsmust meet standards of design that are fundamentally different from keydesign parameters of the safest and most effective tourniquet cuffs.Tourniquet cuffs of the prior art are not designed to serve a sensingpurpose, and blood-pressure cuffs of the prior art are not designed toserve an effector purpose.

The inward compressive force applied to a limb by a pressurizedtourniquet cuff to close underlying arteries is not equal across thewidth of the cuff, from proximal to distal edges. Consequently wheninflated to a minimum pressure required to stop arterial blood flow pastthe distal edge of the tourniquet cuff, arterial blood within the limbstill penetrates beneath the proximal edge of the cuff for some distanceto a location where the arteries become closed. In addition to thepneumatic pressure to which a selected tourniquet cuff is inflated,several variables affect the distance to which arterial blood penetratesbeneath the cuff. These variables include: the patient's limbcharacteristics (for example, limb shape, circumference and soft tissuecharacteristics at the cuff location); characteristics of the selectedtourniquet cuff (for example, cuff design, cuff shape and cuff width);the technique of application of the cuff to the limb (for example, thedegree of snugness or looseness of application and the absence, presenceand type of underlying limb protection sleeve); physiologiccharacteristics of the patient including blood pressure and limbtemperature; the anesthetic technique employed during surgery (forexample, whether a general or regional anesthetic is given, the typesand dosages of anesthetic agents employed and the degree of attentionpaid to anesthetic management); the length of time the tourniquetremains inflated on the limb; changes in limb position during surgery;and any shift in the location of the cuff relative to the limb duringsurgery.

Many studies published in the medical literature have shown that thesafest tourniquet pressure is the lowest pressure that will stop thepenetration of arterial blood past a specific cuff applied to a specificpatient for the duration of that patient's surgery. Such studies haveshown that higher tourniquet pressures are associated with higher risksof tourniquet-related injuries to the patient. Therefore, when atourniquet is used in surgery, surgical staff generally try to use thelowest tourniquet pressure that in their judgment is safely possible.

It is well established in the medical literature that the optimalguideline for setting the pressure of a constant-pressure tourniquet isbased on “Limb Occlusion Pressure” (LOP). LOP can be defined as theminimum pressure required, at a specific time in a specific tourniquetcuff applied to a specific patient's limb at a specific location, tostop the flow of arterial blood into the limb distal to the cuff. LOP isaffected by variables including the patient's limb characteristics,characteristics of the selected tourniquet cuff, the technique ofapplication of the cuff to the limb, physiologic characteristics of thepatient including blood pressure and limb temperature, and otherclinical factors (for example, the extent of any elevation of the limbduring LOP measurement and the extent of any limb movement duringmeasurement). The currently established guideline for setting tourniquetpressure based on LOP is that an additional safety margin of pressure isadded to the measured LOP, in an effort to account for variations inphysiologic characteristics and other changes that may be anticipated tooccur normally over the duration of a surgical procedure.

Some surgical tourniquet systems of the prior art include means tomeasure LOP automatically. Prior-art tourniquet apparatus havingautomatic LOP measurement means are described by McEwen in U.S. Pat. No.5,439,477 and by McEwen and Jameson in U.S. Pat. No. 5,556,415. Suchprior-art systems have included blood flow transducers that employ aphotoplethysmographic principle to sense blood flow in the distal limb,although other transducers have been suggested in the prior art tomeasure blood flow based on other principles. A blood flow transduceremploying the photoplethysmographic principle uses light to indicate thevolume of blood present in a transduced region, consisting of acombination of a residual blood volume and a changing blood volumeresulting from arterial pulsations. An additional predetermined pressuremargin based on recommendations in published surgical literature isadded to the automatically measured LOP to provide a “RecommendedTourniquet Pressure” (RTP), as a guideline to help the surgical staffselect the lowest tourniquet pressure that will safely stop arterialblood flow for the duration of a surgical procedure. Such prior-artsystems allow the surgical staff to select the RTP based on LOP as thetourniquet pressure for that patient, or to select another pressurebased on the physician's discretion or the protocol at the institutionwhere the surgery is being performed.

Despite the improved performance of prior-art apparatus thatautomatically measures LOP, there are three significant limitations. Thefirst limitation is that a separate, complex and costly distal flowsensor is required: the correct application and use of the requireddistal sensor for automatic LOP measurement is dependent on the skill,training and experience of the surgical staff; the sensor must belocated distally on the limb undergoing surgery and this may not bepossible in some instances; in other instances the distal location ofthe sensor requires placement of a non-sterile sensor in or near asterile surgical field and interferes with the pre-surgical preparationof the limb, thus disrupting the pre-surgical workflow and undesirablyincreasing the overall perioperative time and costs.

A second limitation is that the apparatus of the prior art does notmeasure or estimate any changes to LOP that may occur during surgery.The third limitation is that the Recommended Tourniquet Pressure (RTP)is not a personalized tourniquet pressure (PTP) for that individualpatient, and instead is a population estimate equaling the sum of theLOP measured at some time pre-surgically plus a population-based andpredetermined increment of pressure. This increment is set to be anincrement greater than the magnitude of an increase in LOP normallyexpected during surgery, but the amount of increment is based onaggregated data from a population of surgical patients during a widevariety of surgical procedures and is not personalized to an individualpatient undergoing a specific surgical procedure under a specificanesthetic protocol. Accordingly, an RTP of the prior art is not a PTP,and may be higher or lower than optimal.

In U.S. Pat. No. 6,605,103, Hovanes et al. describe apparatus fordetecting the flow of blood past a tourniquet cuff and into a surgicalfield. Such prior-art apparatus is impractical because blood must flowpast the tourniquet cuff before it can be detected, requiring surgicalstaff to do one of two things if blood enters the surgical field:interrupt the surgical procedure and take action to remove the blood; orproceed with blood in the field which might affect visualization and thequality of surgery. Further, Hovanes et al. relies on the accuratesensing of the onset of blood flow past a tourniquet cuff by themeasurement of blood flow-related signals. Such apparatus can only beused when arterial blood is actually flowing past the tourniquet cufftoward the surgical field.

Certain prior-art systems adapt ultrasonic Doppler techniques to sensethe penetration of arterial blood within a portion of a limb beneath anencircling tourniquet cuff. Examples of such systems are described byMcEwen and Jameson in U.S. Pat. No. 8,366,740 and U.S. PatentPublication No. 2013/0144330, and by McEwen et al in U.S. PatentPublication No. 2013/0190806. Detection of arterial blood penetrationwithin a limb beneath a tourniquet cuff by adapting ultrasonic Dopplerapparatus and methods requires the accurate measurement of smallpulsatile signals in the presence of relatively large levels of noise,especially as the amount of arterial blood beneath the cuff decreases.Further, detection of blood penetration by such methods must be rapid aswell as accurate, to facilitate dynamic and accurate control oftourniquet pressure during surgery. Ultrasonic tourniquet systems of theprior art have other significant limitations: the additional ultrasonicsensing arrays required, together with the associated ultrasonic signalprocessing circuitry and software, are costly; also, adapting andincorporating ultrasonic sensing arrays into tourniquet cuffs is complexand costly, and may be prohibitive in view of the fact that competingtourniquet systems employ cuffs that are sterile, low-cost, disposableproducts; further, the safe operation of ultrasonic tourniquet systemsis at present complex and user-dependent, requiring additional usertraining and skill.

Tourniquet systems have also been found to be useful for stoppingarterial blood flow past an applied tourniquet cuff for a variety ofnon-surgical medical procedures. Tourniquet systems may also be used tostop arterial blood flow past an applied cuff applied at regions of apatient other than on the patient's arm or leg. For example, occludingarterial bloodflow to the scalp can be beneficial for reducingchemotherapy-related alopecia, and occluding arterial bloodflow to thehand and foot may be beneficial for reducing nail loss and ‘hand-footsyndrome’ resulting from chemotherapy. Thus, when characterizing theminimum pressure required in a cuff to prevent arterial blood flow pastthe cuff, the more general term Distal Occlusion Pressure (DOP) is usedinstead of LOP.

Some clinicians have found that repeated cycling of a tourniquet cuffapplied to a region of a patient, typically a limb, between a highpressure and zero pressure, i.e., repeated occlusion and reperfusion ofthe vasculature in a limb may improve physiologic parameters such asvasodilation and tissue oxygen utilization. Such intermittent vascularocclusion (IVO) cycles have been shown to accelerate and enhance musclefunction and recovery in certain clinical and rehabilitative settings.However, it is known that unnecessarily high tourniquet pressures arehazardous because they can cause injuries to the nerves muscles andblood vessels underlying, and distal to, a tourniquet cuff. Also, forcertain types of patients and with certain types of narrow cuffs, evenvery high pressures will not achieve vascular occlusion. Further, it isknown that prolonged periods of vascular occlusion can cause seriousinjuries to muscles, nerves, blood vessels and other soft tissues. Thus,there is a need for a personalized tourniquet system that can accuratelyand reliably establish the safest occlusion pressure for each patient,cuff type and location of cuff application, that can repeatedly andautomatically cycle between that personalized occlusion pressure and anon-occlusive pressure in the safest manner possible, and that can beemployed clinically by a user to optimally accelerate and enhance musclefunction and recovery on an individualized basis.

There is a need for a tourniquet system that can establish and maintaina tourniquet pressure that is personalized for each patient, andoptimized for each surgical or medical procedure, and for each appliedtourniquet cuff. Preferably, such a system would be implemented withoutthe need for substantially increased training, knowledge or skill on thepart of the medical staff. There is also a need for a personalizedtourniquet system that overcomes the requirement of the prior art for aseparate, complex and costly distal blood flow sensor or other apparatusfor estimating the patient's limb or distal occlusion pressure before asurgical or medical procedure. Such a system would also overcome therequirement of the prior art for separate, costly and complex apparatusto sense, display, monitor and control the distance of penetration ofarterial blood beneath an applied tourniquet cuff. There is a relatedneed for a personalized tourniquet system having a dual-purposetourniquet cuff wherein the same inflatable bladder of the tourniquetcuff can be separately operated as a patient sensor or as a tourniqueteffector, or simultaneously operated as a combined sensor and effector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of a preferred embodiment in useduring surgery.

FIG. 2 is a block diagram of a preferred embodiment.

FIG. 3 is a detailed block diagram of the effector module.

FIG. 4 is detailed block diagram of the sensor module.

FIGS. 5a, 5b, 5c, and 5d are graphs of pneumatic pulsations and noisesensed by the dual-purpose cuff.

FIGS. 6a, 6b, 6c, 7a, 7b, 8a and 8b show graphical icons that depictchanges in distance of penetration and corresponding physiologicpulsations and reference pulsations.

FIG. 9 is a pictorial representation of a second preferred embodiment inuse during surgery.

FIG. 10 is a block diagram of the second preferred embodiment.

FIG. 11 is a pictorial representation of embodiments in use during amedical procedure for stopping arterial bloodflow into a region of thescalp.

FIG. 12 is a pictorial representation of a representative embodimentadapted to provide intermittent vascular occlusion to two limbs.

FIG. 13 shows a cycle pressure waveform used by the controller toprovide intermittent vascular occlusion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments illustrated are not intended to be exhaustive or limitthe invention to the precise form disclosed. They are chosen anddescribed in order to explain the principles of the invention and itsapplication and practical use, and thereby enable others skilled in theart to utilize the invention.

FIG. 1 depicts the tourniquet system of a preferred embodiment inclinical use for a surgery on a limb or other patient extremity.Tourniquet cuff 2 is shown encircling a patient limb 4 at a locationproximal to surgical site 6 and pneumatically connected to instrument 8.Cuff 2 is a dual-purpose tourniquet cuff that effects the stoppage ofblood penetration past the cuff when inflated and senses changes inblood penetration in the portion of the limb encircled by the cuff whenblood penetration past the cuff is stopped.

Cuff 2 is a type of tourniquet cuff that has common predeterminedparameters that makes it suitable as a dual-purpose cuff including: asingle inflatable bladder having a length sufficient to surround aregion of a patient at a predetermined location; a cuffwidth-to-circumference ratio that is substantially different than othertypes of cuffs such as those approved for blood pressure measurement; acontinuous pneumatic passageway that pneumatically connects a cuff port10 to all parts of the inflatable bladder, and construction, materials,fasteners and design that produce safe low-pressure gradients on tissuesbeneath cuff 2 when cuff 2 is inflated to a level that preventspenetration of arterial blood past cuff 2 for the duration of a surgicalor medical procedure.

A pneumatic passageway between instrument 8 and cuff 2 is provided bycuff port 10, male locking connector 12, female locking connector 14 andflexible tubing 16. Cuff port 10 is of sufficient length to allow apneumatic connection to cuff 2 to be made outside of a sterile surgicalfield. Cuff port 10 is fitted with a male locking connector 12 thatmates to form a releasable pneumatic connection with female lockingconnector 14.

To permit instrument 8 to automatically determine if cuff 2 isacceptable for the dual purposes of sensing blood penetration andeffecting the stoppage of blood penetration past the cuff, male lockingconnector 12 includes indicia that identify the physical characteristicsof cuff 2. In the preferred embodiments the indicia is a distinct colorthat identifies the distinct physical characteristics of cuff 2 toinstrument 8 and to a user of the preferred embodiments.

Female locking connector 14 includes a sensor responsive to the color ofconnector 12 and communicates the detected color information toinstrument 8 when male connector 12 is mated with connector 14 to form apneumatic passageway. It will be appreciated that alternate methods ofautomatically identifying cuff 2 may be used, for example: incorporatingRFID devices into cuff 2 or into connector 12, or configuring the shapeof connectors 12 and 14 so that only dual-purpose cuffs are connectableto instrument 8.

The preferred embodiment shown in FIG. 1 includes a distal bloodtransducer 18 which is shown adapted to be applied to a portion of limb4 distal to cuff 2 and connected to instrument 8 by cable 20. Bloodtransducer 18 is similar in function and construction to the transducerdescribed in U.S. Pat. No. 8,425,426. In a preferred embodiment bloodtransducer 18 is used to automatically determine the Distal OcclusionPressure (DOP) at a time prior to the commencement of a surgical ormedical procedure when blood penetration past the cuff is permitted andwill not interfere with performance of the procedure. The DOP is theminimum level of pressure required in the inflatable bladder of cuff 2to stop arterial blood from penetrating past the region of a patientencircled by cuff 2, i.e., in a direction toward a patient extremity.The DOP is used by the preferred embodiments as described further belowto establish a Personalized Tourniquet Pressure (PTP). A PTP is apatient-specific safe level of pressure greater than DOP to bemaintained in the inflatable bladder of cuff 2 during the period of timethat the surgical or medical procedure is being performed.

Instrument 8 utilizes a graphical touchscreen user interface 22 todisplay information to the user and to permit the user to control theoperation of the preferred embodiments.

A user of the preferred embodiments may initiate or confirm desiredactions to be performed by instrument 8 by touching touchscreen 22within the perimeter of a graphical icon representative of an action tobe performed by instrument 8. For example: a user may: during thepre-surgical time period select to operate cuff 2 as a patient sensor toestimate a Personalized Tourniquet Pressure (PTP); select to operatecuff 2 as an effector to maintain a level of pressure near the estimatedPTP in cuff 2 during surgery; adjust the level of pressure maintained incuff 2; initiate the pressurization of cuff 2; initiate thedepressurization of cuff 2 to a pressure level near zero; set a timelimit for a procedure time alarm; temporarily silence audible alarms;and set other operational parameters of instrument 8. A user may beselectively inhibited from initiating some actions when hazardconditions are detected. Some operations may require the user tocomplete confirmation steps prior to initiating the desired action.

Touchscreen user interface 22 also displays information pertaining tothe operation of instrument 8 to the user. Touchscreen user interface 22may selectively display any of the following information: the level ofpressure within cuff 2 measured by instrument 8 (effector pressure); thepressure level to be maintained in cuff 2 when cuff 2 is inflated(reference pressure level); the length of time that cuff 2 has beeninflated (procedure time); pressure warning indicators; alarm reference“limits” or values; alarm messages describing detected alarm events;icons indicative of blood penetration past the cuff while blood flowpast the cuff is stopped; and other information and instructionspertinent to the operation of instrument 8. To facilitate a clear andrapid understanding of the information presented to the user ofinstrument 8, alphanumeric text, graphic icons, and color may all beused to convey information.

In FIG. 1 touchscreen user interface 22 is shown during the proceduretime period after a Personalized Tourniquet Pressure has beenestablished. A pictorial representation of blood penetration into theregion of a patient encircled by cuff 2 is displayed by touchscreen 22.The pictorial representation of blood penetration shown in FIG. 1consists of: limb segment icon 24, artery icon 26, cuff icon 28, adistance of penetration indicator 30 that indicates the distance ofpenetration of arterial blood into the region of the limb encircled bycuff 2; and a safety margin indicator 32.

The distance of penetration of arterial blood varies over each cardiaccycle, for simplicity, in describing the present invention; the term‘distance of penetration’ is used to refer to the maximum distance ofpenetration during a cardiac cycle.

As described further below the pictorial representation of bloodpenetration past the cuff into the region of the limb encircled by cuff2 is continually updated during the procedure time period so that thedistal edge of indicator 30 and the shape of artery icon 26 representthe current distance of penetration as determined by the preferredembodiments.

A block diagram of a preferred embodiment of instrument 8 is shown inFIG. 2. Referring to FIG. 2, controller 34 is a microcontroller typicalof those known in the art with associated memory, analog, and digitalperipheral interface circuitry, and other support components. Controller34 executes software programs that control the operation of instrument 8as described below. For clarity, and to enable a better understanding ofthe principles of the invention, some functions that are performed bycontroller 34 in conjunction with actuators and transducers aredescribed and shown in FIG. 2 as separate functional blocks. Thesefunction blocks include effector module 36, sensor module 38, cuffidentification module 40, distal blood transducer interface 42 andexternal interface module 44.

Power supply 46 connects to an external AC supply and provides regulatedDC power for the normal operation of all electronic components ofinstrument 8. Power supply 46 also includes a battery to enableinstrument 8 to continue to operate for a period of time in the absenceof an external AC supply.

Speaker 48 is used to alert a user of the preferred embodiments to alarmconditions. Speaker 48 is connected to controller 34. Electrical signalshaving different frequencies to specify different alarm signals andconditions are produced by controller 34 and converted to audible soundby speaker 48.

Instrument 8 may communicate with an external operating room informationsystem or other external device via external interface module 44.External interface module 44 provides the physical communicationinterface such as USB, Ethernet, Bluetooth or Wi-Fi and the appropriatecommunication protocol specific to the connected external device. Datathat may be reported to an external device includes: data and eventsoccurring prior to the commencement of a surgical or medical proceduresuch as the measurement of the minimum pressure required to stop bloodpenetration past cuff 2, cuff pressure level settings, and alarm limitsettings; data and events occurring during a procedure such as: alarmconditions, distances of blood penetration, cuff pressure levels,adjustments to pressure level settings and alarm limit settings.

Cuff identification module 40 communicates wirelessly with color sensorsthat form part of female connector 14. When cuff connector 12 is matedwith connector 14, color sensors within connector 14 determine the colorof connector 12. The color information from the sensors is communicatedto cuff identification module 40.

Cuff identification module 40 maintains a data table that associatescuff connector color with predetermined physical characteristics of theconnected cuff. The characteristics of the connected cuff arecommunicated to controller 34 and used by controller 34 as describedfurther below. An example of a data table maintained by cuffidentification module is shown below in Table 1.

TABLE 1 Connector Dual-Purpose Bladder Bladder Bladder Color Cuff ShapeWidth Length Red Yes Curved 3.25 in.  18 in. Green Yes Curved 3.5 in. 24in. Blue Yes Curved 3.5 in. 34 in. Purple Yes Rectangular 3.75 in.  44in. Yellow Yes Rectangular 1.5 in. 44 in. White No unknown unknownunknown

If the type of cuff connected to instrument 8 is not a dual-purposecuff, controller 34 alerts the user of instrument 8 by displaying awarning message on touchscreen 22 and configures touchscreen 22 toinhibit the selection of the cuff to operate as a sensor and effector.Touchscreen 22 may also be configured to permit a user to override theinhibited selection and permit the cuff to operate as an effector.

Touch screen user interface 22 is similar to the touchscreen userinterface described in U.S. Patent Application No. 20130211445 andincludes features to prevent hazards and suppress inadvertent andunintended actions. Touchscreen user interface 22 communicates withcontroller 34 to initiate actions and receive data for display. Touchscreen user interface 22 also receives distance of penetration data fromsensor module 38 to display in a pictorial representation as shown inFIG. 1.

Blood transducer interface module 42 communicates with blood transducer18 via cable 20 and with controller 34. Blood transducer 18 employs theprinciple of photoplethysmography and responds to arterial blood thatpenetrates past cuff 2. Blood transducer interface module 42 processesthe signals from transducer 18 and produces an indication to controller34 when blood is penetrating past cuff 2. Prior to the commencement ofthe surgical or medical procedure, to determine the minimum pressurelevel required in the inflatable bladder of cuff 2 to stop bloodpenetration past cuff 2 (DOP) controller 34 operates to incrementallyincrease the pressure in the inflatable bladder of cuff 2 until bloodtransducer interface module 42 no longer indicates that blood ispenetrating past cuff 2. The pressure level in the inflatable bladder ofcuff 2 when blood penetration past cuff 2 is no longer detected is theminimum pressure level required to stop blood penetration past cuff 2.

Effector module 36 communicates with controller 34 and communicatespneumatically with the inflatable bladder of cuff 2. Effector module 36is shown in detail in FIG. 3. Referring to FIG. 3, effector module 36includes a pressure regulator 50, an alarm condition detector 52 and aneffector timer 54. Pressure regulator 50 is an assemblage of componentsfor regulating the pressure of air in the inflatable bladder of cuff 2near a reference pressure level communicated from controller 34.Pressure regulator 50 is similar in design and operation to thetourniquet pressure regulator described in U.S. Pat. No. 8,083,763 andincludes a combination of valves and a pressure source for maintainingthe pressure level within the inflatable bladder of cuff 2 near areference pressure level.

During a procedure when cuff 2 is inflated to stop penetration of bloodpast cuff 2, alarm condition detector 52 monitors the operation ofpressure regulator 50 and communicates signals indicative of detectedalarm conditions to controller 34. Alarm conditions detected by alarmcondition detector 52 are: occlusion of the pneumatic passageway betweenpressure regulator 50 and the inflatable bladder of cuff 2 (occlusionalarm); leakage from the inflatable bladder of cuff 2 or the pneumaticpassageway between pressure regulator 50 and the inflatable bladder ofcuff 2 (leak alarm); bladder pressure level too far below the desiredreference pressure level (low pressure alarm); bladder pressure leveltoo far above the desired reference pressure level (high pressurealarm); malfunction of pressure regulator 50 (malfunction alarm). Itwill be appreciated that other alarm conditions relevant to theoperation of pressure regulator 50 may be detected by alarm conditiondetector 52.

Effector timer 54 operates to produce an indication of the length oftime in minutes that the inflatable bladder of cuff 2 has been inflated(procedure time). The procedure time is communicated to controller 34and displayed on touchscreen 22 when cuff 2 is operating as an effectorto prevent blood from penetrating past cuff 2.

Referring to FIG. 2, sensor module 38 communicates pneumatically withthe inflatable bladder of cuff 2 and communicates with controller 34 andtouchscreen user interface 22. Sensor module 38 senses and analyzespneumatic pulsations occurring in the inflatable bladder of cuff 2 toestablish a Personalized Tourniquet Pressure (PTP) and to produce anongoing estimate of the distance of penetration of arterial blood intothe region encircled by cuff 2 while blood penetration past cuff 2 isstopped.

The sensed pneumatic pulsations primarily arise from volume changes inthe region of a patient encircled by cuff 2, and those volume changesare produced by the penetration of arterial blood during each cardiaccycle into, but not past, the region encircled by cuff 2 while theinflatable bladder of cuff 2 is inflated to a level that stops thepenetration of blood past cuff 2. As noted above for simplicity, indescribing the present invention, the term ‘distance of penetration’ isused to refer to the maximum distance of penetration during a cardiaccycle.

Sensor module 38 is shown in detail in FIG. 4. Referring to FIG. 4,pulsation sensor 56 is shown in pneumatic communication with theinflatable bladder of cuff 2. Pulsation sensor 56 is optimized to detectand characterize pneumatic pulsations that are physiologic in origin andcorrespond to blood penetration into the region of a patient encircledby cuff 2 occurring during each cardiac cycle. Levels of pulsationcharacteristics produced by sensor 56 that are indicative of differingdistances of penetration include maximum pulsation amplitude, pulsationarea (integral over a cardiac cycle), and pulsation frequency spectrum.It will be appreciated that other pulsation characteristics may also beproduced by sensor 56.

Sources of noise unique to the perioperative environment that thepreferred embodiments are used in, may produce pressure fluctuations inthe bladder of cuff 2 that are independent of the pneumatic pulsationscorresponding to the penetration of blood into the region of a patientencircled by cuff 2. Some of these noise sources can produce pressurefluctuations that mimic physiologic pulsations associated with bloodpenetration and effect the accuracy of the levels of pulsationcharacteristics produced by pulsation sensor 56. To characterize andquantify the level of noise present while physiologic pressurepulsations are being sensed by pulsation sensor 56 and to betterdiscriminate between physiologic pressure pulsations and pressurefluctuations caused by noise sources and to help ensure accuratecharacterization of pulsations the preferred embodiments include noisesensor 58. Noise sensor 58 communicates pneumatically with the bladderof cuff 2.

Examples of physiologic pneumatic pulsations and pressure fluctuationscaused by various noise sources are shown in FIGS. 5a, 5b, 5c and 5d .FIG. 5a is a graphical representation of physiologic pneumaticpulsations in the absence of noise sources. FIG. 5b is a graphicalrepresentation of physiologic pneumatic pulsations and pulsationsproduced by movement of limb 4. FIG. 5c is a graphical representation ofphysiologic pneumatic pulsations and pulsations produced by shivering ofthe patient. FIG. 5d is a graphical representation of physiologicpneumatic pulsations and pulsations produced by the normal operation ofpressure regulator 50.

Information relating to the physical characteristics of cuff 2 from cuffidentification module 40 may be used by physiologic pulsation sensor 56and noise sensor 58 to better optimize the sensing of physiologicpulsations and to better determine levels of noise.

The levels of characteristics of each sensed physiologic pulsation arecommunicated to pulsation memory 60 and to personalized tourniquetpressure estimator 62 by pulsation sensor 56. The level of noiseassociated with the sensed pulsation is also communicated to memory 60and estimator 62 by noise sensor 58. If the level of noise associatedwith a sensed pulsation exceeds a predetermined threshold the levels ofthe pulsation's characteristics may be rejected by memory 60 andestimator 62. If the number of rejected pulsations exceed apredetermined alert limit within a predetermined alert time period,controller 34 acts to signal the user by displaying an alarm message ontouchscreen 22 and producing an audio tone.

For a sensed pulsation, memory 60 records the levels of pulsation'scharacteristics, the level of noise near the time the pulsation wassensed and the level of pressure in the bladder of cuff 2 near the timewhen the pulsation was sensed. Pulsation memory 60 may record the levelsof pulsation characteristics and associated level of noise andassociated level of pressure in the bladder of cuff 2 for one or moresensed pulsations depending on the operating mode of the preferredembodiments.

In the preferred embodiments personalized tourniquet pressure estimator62 is used to: estimate a Personalized Tourniquet Pressure (PTP),produce ongoing estimates of distance of penetration during theprocedure time period, and establish a margin of safety for the distanceof penetration estimates.

During the period of time prior to the commencement of the surgical ormedical procedure a user of the preferred embodiments may initiate anestimate of PTP via touchscreen user interface 22. If cuffidentification module 40 does not detect an acceptable dual-purpose cuffpneumatically connected to instrument 8, touchscreen 22 inhibits theinitiation of an estimate of PTP.

To establish a Personalized Tourniquet Pressure (PTP) to be maintainedduring the procedure time period, controller 34, sensor module 38 andestimator 62 operate in a preferred embodiment as described in thefollowing sequence:

a) Distal Occlusion Pressure (DOP) is first estimated as described aboveusing blood transducer 18, controller 34 then directs effector module 36to inflate the bladder of cuff 2 to the DOP level.

b) While the level of pressure in the bladder of cuff 2 is near the DOPthe levels of physiologic pulsation characteristics associated with theDOP are recorded in pulsation memory 60, these levels of pulsationcharacteristics associated with DOP are representative of the maximumdistance of penetration of blood into the region of a patient encircledby cuff 2 while blood penetration completely past cuff 2 is stopped.

c) To determine a Personalized Tourniquet Pressure (PTP) level that isgreater than DOP and results in a distance of penetration that is lessthan the maximum distance, estimator 62 retrieves from memory 60 thelevels of pulsation characteristics associated with DOP and computesusing predetermined percentages the levels of pulsation characteristicsthat will correspond to levels of pulsation characteristics detectedwhen the bladder of cuff 2 is at a level of pressure near the PTP.

d) Controller 34 next directs effector module 36 to incrementallyincrease the level of pressure in the bladder of cuff 2 while estimator62 compares the levels of detected pulsation characteristics with thelevels of the previously computed pulsation characteristicscorresponding to the PTP. When the levels of characteristics of detectedpulsations are near the levels of the computed pulsation characteristicsthe level of pressure in the bladder of cuff 2 is near the PTP andcontroller 34 ceases to increment the pressure level in the bladder ofcuff 2. The level of pressure in the bladder of cuff 2 is recorded bycontroller 34 as the estimated PTP.

It will be appreciated that controller 34 may also determine the PTP byincreasing the level of pressure in the bladder of cuff 2 to levelsubstantially greater than the DOP and then incrementally reducing thelevel of pressure in the bladder of cuff 2 until the levels of detectedpulsation characteristics are near the levels of the previously computedpulsation characteristics corresponding to the PTP.

When the estimate of PTP is completed, the estimated PTP recorded bycontroller 34 is displayed on touchscreen user interface 22, and a usermay then select the PTP as the level of pressure to be maintained in thebladder of cuff 2 during the procedure time period.

The predetermined percentages used by estimator 62 to compute pulsationcharacteristics corresponding to the PTP may be a function of themeasured DOP. The predetermined pulsation percentages used by estimator62 may also be dependent upon the characteristics of cuff 2 as reportedby cuff identification module 40. For example, if the measured DOP isless than 140 mmHg a percentage of 50% may be used, if the DOP isgreater or equal to 140 mmHg a percentage of 55% may be used or if thecuff has a length greater than 34 inches a percentage of 60% may beused.

Pulsation characteristics used by estimator 62 in determining a PTP mayinclude one or a combination of maximum pulsation amplitude, pulsationshape, pulsation area (integral) and pulsation frequency spectrum.

To estimate PTP when an estimate of DOP is not available sensor module38 may be configured to analyze the pneumatic physiologic pulsations inthe bladder of cuff 2 as follows:

a) Controller 34 directs effector module 36 to inflate the bladder ofcuff 2 to a predetermined default pressure level chosen to stop thepenetration of blood past the region of a patient encircled by cuff 2and to produce a distance of penetration that is minimal. The distanceof penetration is minimal when a change in the level of pressure in cuff2 or a change in patient blood pressure does not produce a significantchange in the level of the maximum amplitude of sensed pulsations.

b) The maximum amplitude of the detected physiologic pulsationsassociated with the default level of pressure in the bladder of cuff 2are recorded in pulsation memory 60.

c) Estimator 62 then computes as a percentage of the maximum amplitudeof pulsations associated with the default level of pressure the maximumamplitude of a reference pulsation associated with a level of pressurelower than the default level.

d) Controller 34 then directs effector module 36 to decrease the levelof pressure in the bladder of cuff 2 by predetermined increments untilphysiologic pulsations with a maximum amplitude level near the computedmaximum amplitude of the reference pulsation are detected.

e) Estimator 62 computes as a percentage of the maximum amplitude of thereference pulsation the maximum amplitude of pulsations associated withthe PTP.

f) Controller 34 then directs effector module 36 to further decrease thelevel of pressure in the bladder of cuff 2 by predetermined incrementsuntil physiologic pulsations in the bladder of cuff 2 with a maximumamplitude near the maximum amplitude of pulsations associated with thePTP are detected. The level of pressure in the bladder of cuff 2 isrecorded by controller 34 as the estimated PTP.

Estimator 62 also computes a distance of penetration margin of safety.The margin of safety has upper and lower limits in which the estimateddistance of penetration is to be maintained.

Levels of pulsation characteristics associated with the upper and lowerlimits of the margin of safety are predetermined percentage of thelevels of pulsation characteristics associated with the PTP and arecomputed by estimator 62.

If the distance of penetration exceeds the upper limit of the margin ofsafety, too little pressure is being applied by cuff 2 and blood maypenetrate past cuff 2. If the distance of penetration exceeds the lowerlimit more pressure than necessary is being applied by cuff 2 whichincreases the risk of damage to tissues that are encircled by cuff 2.

To permit a better understanding of how controller 34, sensor module 38and estimator 62 operate together to use levels of pulsationcharacteristics to establish a personal tourniquet pressure thefollowing example with sample values for pressure levels, pulsationcharacteristic levels and ratios is provided. In this simplified examplethe maximum pulsation amplitude is the only pulsation characteristicused by estimator 62 in establishing a Personalized Tourniquet Pressure(PTP). Higher levels of maximum pulsation amplitude are associated withgreater distances of penetration. Prior to the commencement of asurgical or medical procedure cuff 2 and blood transducer 18 are appliedto the patient, a measurement of Distal Occlusion Pressure is performedand the DOP is estimated to be 150 mmHg. Cuff 2 is then inflated to 150mmHg and the physiologic pulsations sensed by pulsation sensor 56 arefound to have a maximum amplitude of 4 mmHg. For the DOP of 150 mmHg,estimator 62 selects a predetermined percentage of 60% and calculatesthe maximum amplitude of pulsations occurring at the PersonalizedTourniquet Pressure to be 2.4 mmHg (4*0.6). The level of pressure incuff 2 is increased until physiologic pulsations having a maximumamplitude near 2.4 mmHg are detected. The level of pressure in cuff 2when pulsations with a maximum amplitude near 2.4 mmHg are detected is195 mmHg. 195 mmHg is the Personalized Tourniquet Pressure that is to bemaintained in cuff 2 during the procedure time period. Estimator 62 alsocomputes upper and lower distance of penetration safety margin limitsbased on the maximum amplitude of the pulsations at the PTP, in thisexample estimator 62 uses a percentage 120% for the upper limit and 70%for the lower limit, for maximum pulsation amplitudes of 2.88 mmHg(2.4*1.2) and 1.68 mmHg (2.4*0.7) respectively.

During the procedure time period when instrument 8 is maintaining thelevel of pressure in the bladder of cuff 2 near the PersonalizedTourniquet Pressure estimator 62 operates to produce an estimate of thedistance of penetration of arterial blood past cuff 2 when bloodpenetration past cuff 2 is stopped. Estimator 62 produces this estimateby comparing the levels of pulsation characteristics of the mostrecently detected physiologic pulsation with the levels ofcharacteristics of a reference pulsation recorded in pulsation memory60. The levels of characteristics of the reference pulsation typicallycorrespond to a pulsation occurring when the level of pressure in cuff 2is near the DOP, however it will be appreciated that levels ofcharacteristics of pulsations occurring at other levels of pressure incuff 2 may be used.

The distance of penetration estimate is communicated to touchscreen 22for display to a user. As described above the preferred embodimentsdisplay a pictorial representation of distance of penetration estimatesto better convey this information to a user. FIGS. 6a, 6b, and 6c showtouchscreen 22 displaying pictorial representations of distance ofpenetration and corresponding graphs of associated physiologicpulsations and reference pulsations at various times throughout theprocedure time period while the level of pressure in the bladder of cuff2 is constant. As shown in FIGS. 6a, 6b, and 6c the level of pressure inthe bladder of cuff 2 remains constant.

In FIG. 6a the distal edge of distance of penetration indictor 30 andthe shape of artery icon 24 indicate that the distance of penetration isat a nominal distance. The proximal edge of distance of penetrationindictor 30 lies within the safety margin limits and they are not beingexceeded. The corresponding graph shows a reference physiologicpulsation 602 and the physiologic pulsation 604 associated with thepictorial representation of distance of penetration.

FIG. 6b is illustrative of a decrease in the distance of penetrationcaused by a decrease in the blood pressure of the patient. The distaledge of penetration indicator 30 lies outside the lower safety marginlimit, alarm indicator icon 64 is displayed to alert the user that thesafety margin limits have been exceed. The corresponding graph showsreference pulsation 602 and the physiologic pulsation 606 associatedwith the pictorial representation of distance of penetration. Note thatthe amplitude of associated physiologic pulsation 606 is less than theamplitude of the reference pulsation 602, indicative of a decrease inthe distance of penetration.

FIG. 6c is illustrative of an increase in the distance of penetrationcaused by an increase in the blood pressure of the patient. The distaledge of penetration indicator 30 lies outside the upper safety marginlimit, alarm indicator icon 64 is displayed to alert the user that thesafety margin limits have been exceed. The corresponding graph showsreference pulsation 602 and the physiologic pulsation 608 associatedwith the pictorial representation of distance of penetration. Note thatthe amplitude of the associated pulsation 608 is greater than theamplitude of the reference pulsation 602, indicative of an increase inthe distance of penetration.

FIGS. 7a, 7b, 8a and 8b show touchscreen 22 displaying pictorialrepresentations of distance of penetration and corresponding graphs ofassociated physiologic pulsations and reference pulsations. Thesefigures illustrate the effect of changing cuff pressure on the distanceof penetration.

FIG. 7a is illustrative of a decrease in the distance of penetrationcaused by a decrease in the blood pressure of the patient. The distaledge of penetration indicator 30 lies outside the lower safety marginlimit, alarm icon 64 is displayed to alert the user that the safetymargin limits have been exceed. The level of pressure in the bladder ofcuff 2 (effector pressure) is 250 mmHg. The corresponding graph showsreference pulsation 702 and the physiologic pulsation 704 associatedwith the pictorial representation of distance of penetration. Note thatthe amplitude of associated physiologic pulsation 704 is less than theamplitude of the reference pulsation 702, indicating a decrease thedistance of penetration.

FIG. 7b is illustrative of an increase in the distance of penetrationcaused by a reducing the level of pressure in the bladder of cuff 2. Thedistal edge of penetration indicator 30 lies within the safety marginlimits and alarm icon 64 is not displayed. The level of pressure in thebladder of cuff 2 (effector pressure) has been decreased by a user to200 mmHg. The corresponding graph shows reference pulsation 702 and thephysiologic pulsation 706 associated with the pictorial representationof distance of penetration. Note that the amplitude of associatedphysiologic pulsation 706 is near the amplitude of the referencepulsation 702, indicating that distance of penetration has been restoredto a nominal distance.

FIG. 8a is illustrative of an increase in the distance of penetrationcaused by an increase in the blood pressure of the patient. The distaledge of penetration indicator 30 lies outside the upper safety marginlimit, alarm icon 64 is displayed to alert the user that the safetymargin limits have been exceeded. The level of pressure in the bladderof cuff 2 (effector pressure) is 250 mmHg. The corresponding graph showsreference pulsation 802 and the physiologic pulsation 804 associatedwith the pictorial representation of distance of penetration. Note thatthe amplitude of associated physiologic pulsation 804 is greater thanthe amplitude of the reference pulsation 802, indicating an increase inthe distance of penetration.

FIG. 8b is illustrative of a decrease in the distance of penetrationcaused by an increasing the level of pressure in the bladder of cuff 2.The distal edge of penetration indicator 30 lies within the safetymargin limits and alarm icon 64 is not displayed. The level of pressurein the bladder of cuff 2 (effector pressure) has been increased by auser to 275 mmHg. The corresponding graph shows reference pulsation 802and the physiologic pulsation 806 associated with the pictorialrepresentation of distance of penetration. Note that the amplitude ofassociated physiologic pulsation 806 is near the amplitude of thereference pulsation 802, indicating that distance of penetration hasbeen restored to a nominal distance.

To automatically maintain a safe level of pressure in the inflatablebladder of cuff 2, controller 34 may be configured to regulate the levelof pressure in the bladder of cuff 2 to maintain the distance ofpenetration near a reference level associated with a PTP.

FIGS. 9 and 10 depict the tourniquet system of a second preferredembodiment. FIG. 9 shows the second preferred embodiment in clinical useand FIG. 10 is a block diagram of this embodiment. This second preferredembodiment is similar to the preferred embodiment described above withthe exception that transducer 18 and its related interface do not formpart of this embodiment. In the second preferred embodiment describedbelow sensor module 38 performs additional functions to estimate DistalOcclusion Pressure (DOP) directly by using cuff 2 as a sensor andanalyzing the levels of characteristics of physiologic pulsationsdetected at various levels of pressure in the inflatable bladder of cuff2.

Estimates of DOP and PTP are made during a period of time prior to thecommencement of the surgical or medical procedure. When a user initiatesan estimate of DOP and PTP via touchscreen interface 22, controller 34and sensor module 38 operate as follows:

a) Controller 34 directs effector module 36 to inflate the bladder ofcuff 2 to a predetermined default pressure level chosen to stop thepenetration of blood past the region of a patient encircled by cuff 2and to produce a distance of penetration that is minimal. In thepreferred embodiments the predetermined default pressure level is 300mmHg. It will be appreciated that other default pressure levels may bepredetermined and that the default pressure level may be dependent uponcharacteristics of the cuff connected to instrument 8 as reported bycuff identification module 40. A default pressure level may also beselected by a user of instrument 8 via touchscreen user interface 22.

b) The levels of characteristics of detected physiologic pulsationsassociated with the default level of pressure in the bladder of cuff 2are recorded in pulsation memory 60. The level of noise associated withthe detected pulsations is also recorded in pulsation memory 60.

c) Controller 34 then directs effector module 36 to decrease the levelof pressure in the bladder of cuff 2 by predetermined increments until apredetermined minimum level of pressure is reached. Following eachdecrease in the level of pressure in the bladder of cuff 2, the levelsof characteristics of detected physiologic pulsations, their associatedlevel of noise and associated level of pressure are recorded in memory60. When the predetermined minimum level of pressure has been reachedcontroller 34 directs effector module 36 to deflate the bladder.

d) Estimator 62 then retrieves the levels of pulsation characteristicsand their associated bladder pressure levels from memory 60. Estimator62 compares and analyzes the recorded levels of characteristics todetermine the maximum levels of pulsation characteristics recorded whilethe level of pressure in the bladder of cuff 2 was being decreased.Generally, as the level of pressure in the bladder of cuff 2 isdecreased the depth of penetration of blood into the region encircled bycuff 2 increases and the levels of characteristics of physiologicpulsations also increase. The levels of characteristics of physiologicpulsations are at their maximum levels when the level of pressure in thebladder of cuff 2 is at a pressure that is below DOP and arterial bloodis penetrating past the region of a patient encircled by cuff 2. Levelsof characteristics of pulsations associated with DOP have been found tohave a predetermined relationship with the maximum levels of pulsationcharacteristics that are detected when blood is penetrating past thecuff.

e) After determining the maximum levels of pulsation characteristicsrecorded while the level of pressure in the bladder of cuff 2 wasdecreased from a default level of pressure to a predetermined minimumlevel of pressure, estimator 62 computes, using predeterminedpercentages of the maximum levels the levels of pulsationcharacteristics that will match the levels of pulsation characteristicsdetected when the level of pressure in the bladder of cuff 2 is near theDOP.

f) Estimator 62 analyzes the recorded levels of pulsationcharacteristics and their associated levels of pressure to estimate thepatient's DOP by calculating the level of pressure required in thebladder of cuff 2 to produce pulsations with characteristics that matchthe previously computed levels of pulsation characteristics associatedwith DOP. Estimator 62 also analyzes the recorded levels of noiseassociated with the pulsation characteristics to determine the level ofnoise associated with the DOP estimation. To compensate for any effectsthat noise may have on the accuracy of the DOP estimation, estimator 62uses the estimated DOP and the level of noise associated with the DOPestimation to determine the estimated PTP. The estimated PTP computed byestimator 62 is a function of the estimated DOP and the level of noiseassociated with the DOP estimation. If the level of noise associatedwith the DOP estimation less than a predetermined low noise threshold,PTP is estimated by adding a predetermined pressure increment to theestimated DOP. If the level noise associated with the DOP estimation isgreater than or equal to the low noise threshold and less than apredetermined maximum noise threshold, PTP is estimated by adding apredetermined pressure increment to the estimated DOP that is greaterthan the predetermined increment added when the level of noise is belowthe low noise threshold.

If the level of noise associated with the DOP estimation is greater thanor equal to predetermined maximum noise threshold level, then PTP cannotbe reliably estimated from the estimated DOP and the PTP is set to apredetermined default level, a warning message is displayed ontouchscreen 22 and a warning audio tone is produced to alert the user.

For example if the DOP is estimated to be 140 mmHg and the level ofnoise associated with the estimation is below the low noise thresholdthe PTP will be estimated to be 190 mmHg (140 mmHg+50 mmHg). If thelevel of noise is above the low noise threshold and below the maximumthreshold the PTP will be estimated to be 215 mmHg (140 mmHg+75 mmHg).If the level of noise is greater than the maximum noise threshold theestimated PTP will be a default pressure of 300 mmHg.

It will be appreciated that other functions of estimated DOP andassociated noise levels may be used to estimate a PTP other than thefunction described above.

It will be apparent that to record the levels of pulsationcharacteristics associated with varying levels of pressure in thebladder of cuff 2 between a default pressure and a minimum pressure asequence other than that described above (where the level of pressure isreduced in predetermined amounts from a default level to a minimumlevel) may be used. For example: controller 34 may direct effectormodule 36 to inflate the bladder of cuff 2 to a predetermined minimumlevel and increase the level of pressure in predetermined incrementsuntil a default pressure level is reached; controller 34 may also varythe predetermined increment amount, default level of pressure andminimum level of pressure in response to the magnitude of the levels ofphysiologic pulsation characteristics detected and their associatedlevel of pressure in the bladder of cuff 2.

During the period of time prior to the commencement of a surgical ormedical procedure, a user of the second preferred embodiment selects asuitable dual-purpose tourniquet cuff 2 to encircle a region of apatient to which arterial bloodflow past the cuff is to be stopped, forexample limb 4 proximal to surgery site 6. The user secures the cuffaround the limb and connects it so that the cuff communicatespneumatically with instrument 8. Cuff identification module 40 attemptsto identify the cuff to determine if it is an acceptable dual-purposetourniquet cuff. If the cuff is not an acceptable dual-purpose cuff foruse with the preferred embodiment or it cannot be identified a warningis given to the user via touchscreen user interface 22 and the controlsemployed to initiate an estimate of PTP and to inflate the cuff aredisabled, thereby preventing the use of an unacceptable cuff.

If the pneumatically connected cuff is acceptable a user may initiate anestimate of Personalized Tourniquet Pressure (PTP) by touching acorresponding graphic icon shown on touchscreen user interface 22.

To estimate the PTP, instrument 8 will inflate the bladder of cuff 2 tovarious levels while recording the levels of characteristics ofpneumatic physiologic pulsations associated with the pressure levels asdescribed above. During the estimation an icon representing theestimation's progress will be show on touchscreen 22. If during theestimation of PTP, noise that is independent of arterial bloodpenetration is present, such as noise created by shaving the patient orfrom the patient shivering, and that noise exceeds a predeterminedthreshold, the estimation will be suspended and a warning messagedisplayed touchscreen 22.

When instrument 8 has completed an estimation of PTP, the PTP and DOPare displayed on touchscreen 22 and a user may select the estimated PTPas the level of pressure to maintain in the bladder of cuff 2 during theprocedure time period. To ensure that the estimated PTP remains relevantto the physiologic state of the patient, controller 34 only permits auser to select the estimated PTP as the level of pressure to bemaintained in the bladder of cuff 2 during a procedure for apredetermined period of time after the estimation of PTP has beencompleted. If the PTP is not selected within the predetermined period oftime another estimate of PTP must be initiated or the user must select adefault pressure level to be maintained in the bladder of cuff 2 duringa procedure.

After selecting the level of pressure to be maintained in the bladder ofcuff 2 during the procedure time period the user may initiate thetourniquet effector (inflate cuff 2) by touching an icon on touchscreen22. If the user has selected the previously estimated PTP as the levelof pressure to be maintained in the bladder of cuff 2, instrument 8 willas described above displays icons representing distance of penetration.Sensor module 38 will continually monitor the pneumatic physiologicpulsations arising in the bladder of cuff 2 and display via touchscreen22 an estimate of the distance arterial blood penetrates into the regionof a patient encircled by cuff 2 while the penetration of blood past thecuff is prevented. If the distance of penetration exceeds apredetermined safety margin an alarm message will be shown ontouchscreen 22 and an audio tone will be generated to alert the user tothe potentially unsafe condition. A user may choose to adjust viatouchscreen 22 the level of pressure maintained in the bladder of cuff 2to restore the distance of penetration to within the margin of safety. Auser via touchscreen 22 may configure instrument 8 to automaticallyadjust the level of pressure within the bladder of cuff 2 to maintainthe distance of penetration within the safety margin.

FIG. 11 depicts preferred embodiments in clinical use to stop arterialblood flow into a region or portion of a patient other than an arm or aleg, specifically the scalp. In FIG. 11, dual-purpose tourniquet cuff 2is shown applied to patient head 66 to prevent the flow of arterialblood past cuff 2 into a region of the scalp. Distal blood flow sensor18 is shown adapted for application to the scalp distal to cuff 2, andmay be used prior to the commencement of a surgical or medical procedureas described above to determine a Personalized Tourniquet Pressure. Asfurther described above, cuff 2 may also be used as a sensor todetermine a Personalized Tourniquet Pressure. For example, distal sensor18 or cuff 2 may be used to determine a PTP prior to the administrationof a chemotherapy agent in embodiments used to reduce chemotherapyrelated alopecia.

In FIG. 11, touch screen interface 22 is shown during the procedure timeafter a PTP has been established. A pictorial representation of bloodpenetration into the region of the scalp encircled by cuff 2 isdisplayed. The pictorial representation of blood penetration consists ofhead icon 68, artery icon 70, cuff icon 72, distance of penetrationindicator 74 and safety margin indicator 76. As described further above,the pictorial representation of blood penetration past the cuff into theregion of the scalp encircled by cuff 2 is continually updated duringthe procedure time period so that the distal edge of indicator 74 andthe shape of artery icon 70 represent the current distance ofpenetration as determined by preferred embodiments.

The first or second embodiments described above may be adapted tointermittently occlude the vasculature of region(s) or portion(s) of apatient. Intermittent vascular occlusion (IVO) has been shown toaccelerate and enhance muscle function and recovery in certain clinicaland rehabilitative settings. IVO is the repeated cycling of a tourniquetcuff applied to a region of a patient, typically a limb, between a highpressure and zero pressure. FIGS. 12 and 13 show embodiments adapted forintermittent vascular occlusion. An example of the implementation of thepreferred embodiments adapted for intermittent vascular occlusion is asfollows:

a) Cuff 2 is applied to a patient's limb 4 and the patient's DOP and PTPmay be measured and estimated, respectively, as described in thepreferred embodiments. Alternatively, for practical reasons, the usermay interact with touchscreen user interface 22 to override theestimation of DOP and manually select a PTP pressure level. Suchcircumstances may occur for example: (1) if the user determines PTPusing sensors that are not part of instrument 8, (2) if blood transducer18 could not measure DOP due to the patient missing distal digits orhaving poor circulation, (3) if physiologic pulsation sensor 56 couldnot measure pulsation characteristics due to low pulsation signals andhigh noise from the patient, or (4) if time does not permit themeasurement of DOP and the estimation of PTP. In this example, the DOPis measured to be 150 mmHg and the PTP is set to 165 mmHg (110% of DOP).

b) The user operates the touchscreen user interface 22 of instrument 8to start an intermittent vascular occlusion session and produce one ormore of vascular occlusion cycles 108. The number of vascular occlusioncycles to be delivered may be selected by a user or determined byphysiologic sensor 106 as described further below. Controller 34communicates with effector module 36 to inflate cuff 2 to a firstpressure level near PTP (165 mmHg) during a first time period 110 (5minutes) to occlude the vasculature of a region of limb 4. At the end ofthe first time period 110, effector module 36 reduces the pressure incuff 2 to a second pressure level near 0 mmHg during a second timeperiod 112 (3 minutes) during which arteries and veins in limb 4 are notoccluded. The durations of the first time period 110 and second timeperiod 112 may be pre-programmed, selected by the user via touchscreenuser interface 22, or determined by measured physiologic parameters. ThePTP may be selected to be greater than or equal to DOP to apply botharterial and venous occlusion, or the PTP may be selected to be lessthan DOP to apply arterial restriction and venous occlusion. The secondpressure level may be a non-occlusive pressure that is less than avenous occlusion pressure. If the PTP, duration of the first time period110, duration of the second time period 112, or the number of occlusioncycles exceeds maximum safe limits, instrument 8 and touchscreen userinterface 22 will produce an alarm. When the occlusion cycles have beencompleted, effector module 36 automatically deflates cuff 2 to apressure near 0 mmHg.

c) Before, during or at the end of the intermittent vascular occlusionsession, the user may operate touchscreen user interface 22 ofinstrument 8 to input the values of physiologic parameters indicative ofthe efficacy of the IVO in achieving the desired clinical effect.Physiologic parameters may include but is not limited to the patient'sheart rate, oxygenation level, and creatine kinase level. Physiologicparameters may be used to evaluate the efficacy of the IVO session andprovide feedback to the IVO protocol. For example, based on the efficacydata, the duration of the first time period 110 may be increased by 2minutes (to 7 minutes), and/or PTP may be increased to 195 mmHg (130% ofDOP) for future cycles or sessions. Other changes to the protocol mayresult from the efficacy feedback, such as the duration of the secondtime period 112, number of IVO cycles, and second pressure level. Aphysiologic sensor 106 to measure one or more physiologic parametersrelevant to IVO may be incorporated in instrument 8 to provide feedbackto controller 34 to allow automatic adaptation of IVO protocolparameters.

Instrument 8 may be further adapted to control the pressure in anadditional cuff 102 to provide IVO to an additional limb 104, as shownin FIG. 12. It will be apparent that instrument 8 may be adapted toconnect to a plurality of cuffs to provide IVO to a plurality of regionsof a patient, such as both arms and both legs. Each cuff may cyclebetween the first level of pressure near PTP and a second, non-occlusivelevel of pressure in a synchronous or alternating mode. In thesynchronous mode, each cuff enters each IVO cycle at the same time. Inthe alternating mode, each cuff may enter IVO cycles at different times.It will be apparent that each cuff may be pre-programmed oruser-selected to use different PTPs, length of first time period 110 andlength of second time period 112. More generally, a cycle pressurewaveform, such as a representative cycle pressure waveform 114 and/orany other suitable waveforms, can be stored in memory and accessed bythe controller 34. The cycle pressure waveform 114 defines a desiredlevel of pressure at each time during a cycle time period, and thecontroller may use the stored cycle pressure waveform 114 to maintainthe pressure in at least one applied tourniquet cuff near the levelcorresponding to the desired level of pressure during the cycle timeperiod.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. An apparatus for intermittent vascular occlusion based on apersonalized tourniquet pressure (PTP), comprising: a dual-purposetourniquet cuff having an inflatable bladder adapted to encircle aportion of a patient; a sensor module having a pulsation sensorcommunicating pneumatically with the inflatable bladder of thedual-purpose cuff for sensing and characterizing pressure pulsationsindicative of a distal occlusion pressure (DOP), thereby to identify aminimum pressure at which penetration of blood past the cuff is stopped;a PTP estimator responsive to the pulsation sensor for producing anestimate of a PTP, wherein the estimate of the PTP is a function of theDOP; an effector module communicating pneumatically with the inflatablebladder of the dual-purpose cuff for maintaining pressure in the bladdernear the PTP during a first time period and for maintaining pressure inthe bladder near a second level of pressure during a second time period;and a controller selectively operating the inflatable bladder inconjunction with the sensor module and the effector module.
 2. Theapparatus of claim 1, wherein the duration of the first and second timeperiods are predetermined.
 3. The apparatus of claim 1, wherein theduration of the first and second time periods may be selected by a user.4. The apparatus of claim 1, wherein the function provides a PTP that isat least equal to the DOP.
 5. The apparatus of claim 1, wherein thefunction provides a PTP that is less than the DOP.
 6. The apparatus ofclaim 1, wherein the second level of pressure is non-occlusive.
 7. Theapparatus of claim 1, wherein the effector module further maintainspressure in the bladder during a plurality of intermittent vascularocclusion cycles, each cycle comprising a first cycle time period whenpressure in the bladder is maintained near the PTP and a second cycletime period when pressure is maintained near the second level.
 8. Theapparatus of claim 7, comprising a physiologic sensor for sensing andcharacterizing a parameter indicative of efficacy of the intermittentvascular occlusion cycles on the patient's physiology and wherein theeffector module is further responsive to the physiologic sensor, therebyadapting the duration of the first cycle time period in response to theparameter.
 9. The apparatus of claim 7, comprising a physiologic sensorfor sensing and characterizing a parameter indicative of efficacy of theintermittent vascular occlusion cycles on the patient's physiology andwherein the effector module is further responsive to the physiologicsensor, thereby adapting the number of the plurality of cycles inresponse to the parameter.
 10. The apparatus of claim 7, comprising acycle alarm to alert a user if the plurality of vascular occlusioncycles exceeds a maximum safe number of cycles.
 11. The apparatus ofclaim 7, comprising a physiologic sensor for sensing and characterizinga parameter of efficacy of the intermittent vascular occlusion cycles onthe patient's physiology and wherein the effector module is furtherresponsive to the physiologic sensor, thereby adapting the PTP inresponse to the parameter.
 12. The apparatus of claim 1, wherein theeffector module further communicates pneumatically with at least oneadditional pneumatic cuff applied to the patient and further maintainsthe pressure in the additional cuff near the PTP during the first timeperiod and further maintains the pressure in the additional cuff nearthe second level during the second time period.
 13. The apparatus ofclaim 1, wherein the effector module further communicates pneumaticallywith at least one additional pneumatic cuff applied to the patient andfurther maintains the pressure in the additional cuff near the PTPduring a third time period and further maintains the pressure in theadditional cuff near the second level during a fourth time period. 14.The apparatus of claim 1, wherein the PTP estimator further comprises auser override switch, thereby allowing a user to manually select a levelof pressure for the PTP.
 15. The apparatus of claim 1, comprising a timealarm to alert a user if the duration of the first time period exceeds amaximum safe time limit.
 16. The apparatus of claim 1, comprising apressure alarm to alert a user if the PTP exceeds a maximum safepressure limit.
 17. A method for providing intermittent vascularocclusion based on a personalized tourniquet pressure (PTP), comprising:providing a dual-purpose tourniquet cuff having a pneumatic bladder,wherein the dual-purpose cuff is configured as a sensor and an effectorand to be applied to a patient at a desired location; sensing andcharacterizing pressure pulsations indicative of a distal occlusionpressure (DOP) at the location that is indicative of a minimum pressurein the bladder at which penetration of blood past the tourniquet cuff isstopped; establishing a PTP that is a function of the DOP; establishinga non-occlusive level of pressure near zero; maintaining a pressure inthe cuff near the PTP during a first time period; and at the end of thefirst time period, reducing the pressure in the cuff to thenon-occlusive level and maintaining the pressure in the cuff near thenon-occlusive level during a second time period.
 18. The method of claim17, wherein the function provides a PTP that is at least equal to theDOP.
 19. The method of claim 17, wherein the function provides a PTPthat is less than the DOP.
 20. The method of claim 17, comprisingenabling a user to override the estimation of the DOP by the sensormodule and to set the PTP to a level of pressure selected by the user.21. The method of claim 17, comprising configuring the controller toproduce a plurality of intermittent vascular occlusion cycles, eachcycle comprising a first cycle time period when pressure in the bladderis maintained near the PTP and a second cycle time period when pressureis maintained near the non-occlusive level.
 22. An apparatus forproviding intermittent vascular occlusion based on a personalizedtourniquet pressure (PTP), comprising: a sensor module for estimating adistal occlusion pressure (DOP) by sensing and characterizing pressurepulsations indicative of the DOP to identify an estimated DOP equal to aminimum pressure at which penetration of blood past at least one applieddual-purpose tourniquet cuff is stopped, the dual-purpose cuff beingconfigured as a sensor and an effector; a controller for establishing aPTP that is a function of the DOP, wherein the controller includes auser interface configured to enable a user to override the estimation ofthe DOP by the sensor module by setting the PTP to a level of pressureselected by the user; and an effector module operable for maintaining apressure in the applied tourniquet cuff between the PTP and thenon-occlusive level according to a cycle pressure waveform during eachof a plurality of cycle time periods.
 23. The apparatus of claim 22,comprising a physiologic sensor for sensing and characterizing aparameter indicative of efficacy of the intermittent vascular occlusionon the patient's physiology and wherein the effector module is furtherresponsive to the physiologic sensor to adapt the operation of theeffector module.